Horizon Exceptions

Exceptions raised by the Horizon code and the machinery for handling them.

exception horizon.exceptions.AlreadyExists(name, resource_type)[source]

API resources tried to create already exists.

exception horizon.exceptions.BadRequest[source]

Generic error to replace all “BadRequest”-type API errors.

exception horizon.exceptions.ConfigurationError[source]

Exception to be raised when invalid settings have been provided.

exception horizon.exceptions.Conflict[source]

Generic error to replace all “Conflict”-type API errors.

exception horizon.exceptions.GetFileError(name, resource_type)[source]

Exception to be raised when the value of get_file is not expected.

The expected values start with https:// or http://. Otherwise this exception will be raised.

exception horizon.exceptions.HandledException(wrapped)[source]

Used internally to track exceptions that are already handled.

It is used to track exceptions that have gone through horizon.exceptions.handle() more than once.

exception horizon.exceptions.HorizonException[source]

Base exception class for distinguishing our own exception classes.

class horizon.exceptions.HorizonReporterFilter[source]

Error report filter that’s always active, even in DEBUG mode.


This filter is to add safety in production environments (i.e. DEBUG is False). If DEBUG is True then your site is not safe anyway. This hook is provided as a convenience to easily activate or deactivate the filter on a per request basis.

exception horizon.exceptions.Http302(location, message=None)[source]

Exception used to redirect at the middleware level.

This error class which can be raised from within a handler to cause an early bailout and redirect at the middleware level.

exception horizon.exceptions.MessageFailure[source]

Exception raised during message notification.

exception horizon.exceptions.NotAuthenticated[source]

Raised when a user is trying to make requests and they are not logged in.

The included HorizonMiddleware catches NotAuthenticated and handles it gracefully by displaying an error message and redirecting the user to a login page.

exception horizon.exceptions.NotAuthorized[source]

User tries to access a resource without sufficient permissions.

Raised whenever a user attempts to access a resource which they do not have permission-based access to (such as when failing the require_perms() decorator).

The included HorizonMiddleware catches NotAuthorized and handles it gracefully by displaying an error message and redirecting the user to a login page.

exception horizon.exceptions.NotAvailable[source]

Exception to be raised when something is not available.

exception horizon.exceptions.NotFound[source]

Generic error to replace all “Not Found”-type API errors.

exception horizon.exceptions.RecoverableError[source]

Generic error to replace any “Recoverable”-type API errors.

exception horizon.exceptions.ServiceCatalogException(service_name)[source]

A requested service is not available in the ServiceCatalog.

ServiceCatalog is fetched from Keystone.

exception horizon.exceptions.WorkflowError[source]

Exception to be raised when something goes wrong in a workflow.

exception horizon.exceptions.WorkflowValidationError[source]

Exception raised during workflow validation.

It is raised if required data is missing, or existing data is not valid.

horizon.exceptions.handle(request, message=None, redirect=None, ignore=False, escalate=False, log_level=None, force_log=None, details=None)[source]

Centralized error handling for Horizon.

Because Horizon consumes so many different APIs with completely different Exception types, it’s necessary to have a centralized place for handling exceptions which may be raised.

Exceptions are roughly divided into 3 types:

  1. UNAUTHORIZED: Errors resulting from authentication or authorization problems. These result in being logged out and sent to the login screen.

  2. NOT_FOUND: Errors resulting from objects which could not be located via the API. These generally result in a user-facing error message, but are otherwise returned to the normal code flow. Optionally a redirect value may be passed to the error handler so users are returned to a different view than the one requested in addition to the error message.

  3. RECOVERABLE: Generic API errors which generate a user-facing message but drop directly back to the regular code flow.

All other exceptions bubble the stack as normal unless the ignore argument is passed in as True, in which case only unrecognized errors are bubbled.

If the exception is not re-raised, an appropriate wrapper exception class indicating the type of exception that was encountered will be returned. If details is None (default), take it from exception sys.exc_info. If details is other string, then use that string explicitly or if details is empty then suppress it.